Elevator equipment is located in either hoistway or the machine room. In addition to a car, counterweight, and ropes, the hoistway contains many components that are essential to the safety and performance of the elevator. These include car and counterweight guide rails, pit equipment, a car position reader, hoistway doors, and top and bottom terminal landing limit switches.
Limit switches are mounted on brackets attached to car guide rails at the top and bottom terminal landings in the hoistway. The limit switches are actuated ("opened") by a cam that rides with the car to ensure that the car does not collide with the overhead hoistway structure or compress the elevator buffer.
In a typical mid-rise installation, four limit switches are located at each terminal landing. The first two are slowdown limit switches that are opened before the car reaches the landing. A third limit switch is located at the landing and opens to provide a signal to prevent further travel of the car beyond the landing. A fourth and final limit switch is opened when the car passes the terminal landing and provides a signal to prevent all further travel in either direction.
In some high-rise, high-speed installations, the switches may be mounted on the car. The switches are opened sequentially by cams located at the top and bottom terminal landings.
Existing elevator limit switches have an abundance of parts, are noisy due to the backlash inherent in the assembled parts, are difficult to assemble, inclined to rust, and relatively vulnerable to dust or water.